DEV Community

Cover image for 2181. Merge Nodes in Between Zeros
MD ARIFUL HAQUE
MD ARIFUL HAQUE

Posted on • Edited on

1

2181. Merge Nodes in Between Zeros

2181. Merge Nodes in Between Zeros

Medium

You are given the head of a linked list, which contains a series of integers separated by 0's. The beginning and end of the linked list will have Node.val == 0.

For every two consecutive 0's, merge all the nodes lying in between them into a single node whose value is the sum of all the merged nodes. The modified list should not contain any 0's.

Return the head of the modified linked list.

Example 1:

ex1-1

  • Input: head = [0,3,1,0,4,5,2,0]
  • Output: [4,11]
  • Explanation: The above figure represents the given linked list. The modified list contains
    • The sum of the nodes marked in green: 3 + 1 = 4.
    • The sum of the nodes marked in red: 4 + 5 + 2 = 11.

Example 2:

ex2-1

  • Input: head = [0,1,0,3,0,2,2,0]
  • Output: [1,3,4]
  • Explanation: The above figure represents the given linked list. The modified list contains
    • The sum of the nodes marked in green: 1 = 1.
    • The sum of the nodes marked in red: 3 = 3.
    • The sum of the nodes marked in yellow: 2 + 2 = 4.

Constraints:

  • The number of nodes in the list is in the range [3, 2 * 105].
  • 0 <= Node.val <= 1000
  • There are no two consecutive nodes with Node.val == 0.
  • The beginning and end of the linked list have Node.val == 0.

Solution:

/**
 * Definition for a singly-linked list.
 * class ListNode {
 *     public $val = 0;
 *     public $next = null;
 *     function __construct($val = 0, $next = null) {
 *         $this->val = $val;
 *         $this->next = $next;
 *     }
 * }
 */
class Solution {

    /**
     * @param ListNode $head
     * @return ListNode
     */
    function mergeNodes($head) {
        $dummy = new ListNode(0);
        $current = $dummy;
        $sum = 0;

        // Skip the first zero node
        $head = $head->next;

        while ($head !== null) {
            if ($head->val == 0) {
                $current->next = new ListNode($sum);
                $current = $current->next;
                $sum = 0;
            } else {
                $sum += $head->val;
            }
            $head = $head->next;
        }

        return $dummy->next;
    }
}
Enter fullscreen mode Exit fullscreen mode

Contact Links

If you found this series helpful, please consider giving the repository a star on GitHub or sharing the post on your favorite social networks 😍. Your support would mean a lot to me!

If you want more helpful content like this, feel free to follow me:

Postmark Image

Speedy emails, satisfied customers

Are delayed transactional emails costing you user satisfaction? Postmark delivers your emails almost instantly, keeping your customers happy and connected.

Sign up

Top comments (0)

Billboard image

Create up to 10 Postgres Databases on Neon's free plan.

If you're starting a new project, Neon has got your databases covered. No credit cards. No trials. No getting in your way.

Try Neon for Free →